Known variable flow hydraulic pumps use an auxiliary hydraulic control piston or an electromechanical controller to control the flow rate for the pump. Feedback for control of the piston is typically provided by down-stream (of the pump outlet) measurements of pressure or flow. However, pressure in the control piston is affected by the overall pressure in the hydraulic system, for example to due to activation of various hydraulic components. Changes in the overall pressure cause deviations in the position of the piston, which in turn affects the flow rate of the pump. The control piston can be made more precise by using an electromechanical actuator, but the control loop still has errors and lag induced by the down-stream measurement of pressure or flow. Thus, it is difficult to quickly and accurately attain or maintain a desired flow rate for known variable flow hydraulic pumps.